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Aims: The aim of this work is the development of a mechanistic physiologically‐based pharmacokinetic (PBPK) model using in vitro to in vivo extrapolation to conduct a drug‐drug interaction (DDI) assessment of treosulfan against two cytochrome p450 (CYP) isoenzymes and P‐glycoprotein (P‐gp) substrates. Methods: A PBPK model for treosulfan was developed de novo based on literature and unpublished clinical data. The PBPK DDI analysis was conducted using the U.S. Food and Drug Administration (FDA) DDI index drugs (probe substrates) midazolam, omeprazole and digoxin for CYP3A4, CYP2C19 and P‐gp, respectively. Qualified and documented PBPK models of the probe substrates have been adopted from an open‐source online model database. Results: The PBPK model for treosulfan, based on both in vitro and in vivo data, was able to predict the plasma concentration‐time profiles and exposure levels of treosulfan applied for a standard conditioning treatment. Medium and low potentials for DDI on CYP3A4 (maximum area under the concentration‐time curve ratio (AUCRmax = 2.23) and CYP2C19 (AUCRmax = 1.6) were predicted, respectively, using probe substrates midazolam and omeprazole. Treosulfan was not predicted to cause a DDI on P‐gp. Conclusion: Medicinal products with a narrow therapeutic index (eg, digoxin) that are substrates for CYP3A4, CYP2C19 or P‐gp should not be given during treatment with treosulfan. However, considering the comprehensive treosulfan‐based conditioning treatment schedule and the respective pharmacokinetic properties of the concomitantly used drugs (eg, half‐life), the potential for interaction on all evaluated mechanisms would be low (AUCR < 1.25), if concomitantly administered drugs are dosed either 2 hours before or 8 hours after the 2‐hour intravenous infusion of treosulfan. [ABSTRACT FROM AUTHOR]

Aims Methods Results Conclusion Allogeneic haematopoietic stem cell transplantation (allo‐HSCT) is a vital treatment for various paediatric malignant and nonmalignant diseases. The conditioning treatment before allo‐HSCT is crucial for successful engraftment. Treosulfan, a cytotoxic prodrug, has gained popularity due to its lower toxicity compared to traditional alkylating agents used for conditioning treatment.We investigated the relationship between pharmacokinetics and pharmacodynamics of treosulfan in paediatric patients, in a substudy pooling from 2 multicentre phase 2 clinical trials. A total of 83 children with malignant and nonmalignant diseases received treosulfan‐based conditioning. Treosulfan exposure and its relationship with clinical outcomes, including survival, graft failure and graft‐vs.‐host disease, were investigated.Our findings reveal no significant association between treosulfan exposure and the key clinical outcomes or toxicity (P‐values between .22 and .99), if the dosing is based on the approved product information.These findings suggest that treosulfan exposure after standardized body surface area‐based dosing is appropriate in paediatric allo‐HSCT. [ABSTRACT FROM AUTHOR]

Background: An alternative reduced-toxicity conditioning regimen for allogeneic transplantation, based on treosulfan and fludarabine, has recently been identified. The rationale for this study was to investigate the efficacy and safety of this regimen prospectively in patients with a primary myelodysplastic syndrome., Design and Methods: A total of 45 patients with primary myelodysplastic syndromes were conditioned with 3×14 g/m(2) treosulfan and 5×30 mg/m(2) fludarabine followed by allogeneic hematopoietic stem cell transplantation. Subtypes of myelodysplastic syndromes were refractory anemia with excess blasts-2 (44%), refractory cytopenia with multilineage dysplasia (27%), refractory anemia (9%), refractory anemia with ringed sideroblasts (4%), refractory cytopenia with multilineage dysplasia and ringed sideroblasts (4%), refractory anemia with excess blasts-1 (2%), and myelodysplastic syndrome with isolated del (5q) (2%). The myelodysplastic syndrome was unclassified in 7% of the patients. Forty-seven percent of the patients had a favorable karyotype, 29% an unfavorable one, and 18% an intermediate karyotype. Patients were evaluated for engraftment, adverse events, graft-versus-host disease, non-relapse mortality, relapse incidence, overall survival and disease-free survival., Results: All but one patient showed primary engraftment of neutrophils after a median of 17 days. Non-hematologic adverse events of grade III-IV in severity included mainly infections and gastrointestinal symptoms (80% and 22% of the patients, respectively). Acute graft-versus-host disease grade II-IV developed in 24%, and extensive chronic graft-versus-host disease in 28% of the patients. After a median follow-up of 780 days, the 2-year overall and disease-free survival estimates were 71% and 67%, respectively. The 2-year cumulative incidences of non-relapse mortality and relapse were 17% and 16%, respectively., Conclusions: Our safety and efficacy data suggest that treosulfan-based conditioning therapy is a promising treatment option for patients with myelodysplastic syndromes. clinicaltrials.gov identifier: NCT01062490.